Speed control of variable-speed multiple-phase motors

ABSTRACT

Exemplary embodiments or implementations are disclosed of methods, apparatus, and systems for operating motors in variable speed situations. In an exemplary implementation, a method of controlling a variable-speed motor includes defining a control duration as a predetermined number of cycles of a multiple-phase power supply. Each speed in a range of speeds is defined by a corresponding number of the cycles of the control duration. Power is provided to the motor from the power supply at a selected one of the speeds, by enabling input from the power supply for the number of the cycles of the control duration corresponding to the selected speed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/548,560 filed on Jul. 13, 2012, which claims the benefit and priorityof Chinese Patent of Invention Application No. 201210050377.9 filed Feb.29, 2012. The entire disclosures of the above applications areincorporated herein by reference.

FIELD

The present disclosure relates to systems and methods for speed controlof variable-speed multiple-phase motors.

BACKGROUND

This section provides background information related to the presentdisclosure which is not necessarily prior art.

Blowers in tobacco and/or other food curing barns tend to be three-phasesquirrel-cage type motors. In various phases of tobacco curing, thecubic feet per meter (CFM) needed may vary.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

Exemplary embodiments or implementations are disclosed of methods,apparatus, and systems for operating motors in variable speedsituations. An exemplary implementation is directed to a method ofcontrolling a variable-speed motor. In this example, a control durationis defined as a predetermined number of cycles of a multiple-phase powersupply. Each speed in a range of speeds is defined by a correspondingnumber of the cycles of the control duration. Power is provided to themotor from the power supply at a selected one of the speeds, by enablinginput from the power supply for the number of the cycles of the controlduration corresponding to the selected speed.

Another exemplary implementation is directed to a method of controllinga variable-speed motor. In this example, a frequency of a multiple-phasepower supply is used to define a control duration having a fixed numberof cycles. Each of a plurality of speeds is defined as a correspondingnumber of the cycles of the control duration. Power is provided to themotor from the power supply at a selected one of the speeds, by drivinga signal configured in accordance with the frequency to enable inputfrom lines of the power supply for the number of cycles of the controlduration corresponding to the selected speed.

Another exemplary embodiment is directed to a system for controlling avariable-speed motor. In this exemplary embodiment, a controller isconfigured to provide a driver signal in accordance with a frequency ofa multiple-line, multiple-phase power supply to the motor. An interfacecircuit between an input and load of each line is configured to detectzero crossings in the corresponding line, and to enable or disable powerthrough the corresponding line at the zero crossings based on the driversignal.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1 is a diagram of an exemplary multiple-phase voltage signalconfigured in accordance with an exemplary implementation of the presentdisclosure;

FIG. 2 is a diagram of a system for controlling a variable-speed motorin accordance with an exemplary implementation of the disclosure;

FIG. 3 is a timing diagram of driver signals that may be provided by amotor control system in accordance with an exemplary implementation ofthe disclosure;

FIG. 4 is a diagram of a frequency sensor circuit of a system forcontrolling a variable-speed motor in accordance with an exemplaryimplementation of the disclosure;

FIG. 5 is a flow diagram of a method of controlling a driver signal inaccordance with an exemplary implementation of the disclosure;

FIG. 6 is a perspective view of a drying unit in accordance with anexemplary implementation of the disclosure; and

FIGS. 7 and 8 are diagrams of a drying unit in accordance with exemplaryimplementations of the disclosure.

Corresponding reference numerals indicate corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION

Example embodiments will now be described more fully with reference tothe accompanying drawings.

Blowers in tobacco or other food curing barns normally are three-phasesquirrel cage type motors. In different phases of tobacco curing, thecubic feet per minute (CFM) needed for drying can vary. Thus, in acuring system design, a variable speed blower can be highly useful.

In various exemplary embodiments of the disclosure, full-wave cyclecontrol is used. For example, an exemplary embodiment of a method forvariable speed control of a three-phase motor uses full-wave sinecontrol. In this example, a triac may be triggered at each Zero-Crosspoint. Due to the characteristic behavior of triacs, it will self-turnoff at next Zero-Cross. One can select every eight (8) full sine wavesas a control duration. One can control how many cycles are to be ON andthe rest to be OFF. In this exemplary way, the RMS (root mean square)voltage supplied to a three-phase motor can vary from 1/8 minimum to 8/8full output.

An exemplary embodiment of the present disclosure is directed to amethod for varying the speed of a multiple-phase (e.g., three-phasemotor), for example, from one up to eight stages. Although variousaspects of the disclosure are described with reference to drying barnsand blower motors, the disclosure is not so limited. Aspects of thedisclosure may be practiced in connection with various types ofvariable-speed motors and various environments in which variable-speedmotors may be used, such as applications that use three-phase blowersfor air circulation. Further, exemplary embodiments also arecontemplated in which input power may be provided in fewer than or morethan three phases.

One implementation of a method of controlling a variable-speed motorincludes defining a control duration as a predetermined number of cyclesof a multiple-phase power supply. Each speed in a range of speeds isdefined by a corresponding number of the cycles of the control duration.Power is provided to the motor from the power supply at a selected oneof the speeds, by enabling input from the power supply for the number ofthe cycles of the control duration corresponding to the selected speed.This speed control may be provided at lower cost than inverter-typecontrol, produces little or no harmonic noise, can reduce powerconsumption, and is highly reliable.

With reference to the figures, FIG. 1 is a diagram of an exemplarymultiple-phase voltage signal 20 configured in accordance with the abovemethod. The signal 20 is obtained from a three-phase voltage input,e.g., about 240 VAC at a frequency of about 50 hertz. Accordingly,phases 22, 24, and 26 of the voltage signal 20 are separated by 120degrees and have a frequency of 50 hertz (50 cycles per second). Thus,each full-wave cycle 30 of a phase 22, 24, and 26 lasts for twenty (20)milliseconds.

In one implementation of the disclosure, the signal 20 is driven by amotor control system driver signal as further described below. A controlduration 32 is defined for the driver signal as the duration of twofull-wave cycles of the power supply from which the signal 20 isobtained. Thus, the signal 20 is driven for a control duration 32 forforty (40) milliseconds. A cycle 30 of the signal 20 exhibits zerovoltage crossings 36 at a beginning 40, middle 42, and end 44 of thecycle 30. Each phase of the power supply is driven to alternate betweencompleting a full-wave cycle 30 that reaches peak voltages 48 a and 48b, and a cycle 50 during which the voltage is kept at zero volts. Thesignal of each phase 22, 24, and 26 is repeated every two cycles. Thesignal 20 provides half the RMS voltage otherwise available from itsthree-phase power supply.

In one implementation, the motor control system, further describedbelow, provides the signal 20 to operate a three-phase variable-speedmotor. The motor could be operated at each of two speeds: at full speedin which the full alternating voltage input from the power supply isprovided during both cycles of the control duration 32, or at half-speedas exhibited by the signal 20.

FIG. 2 is a diagram of an exemplary embodiment of a system 100 forcontrolling a variable-speed motor. The system 100 may be configured,e.g., to provide the voltage signal 20 shown in FIG. 1. Additionally oralternatively, the system 100 is configurable to provide various signalsto provide various ranges of power and speed, e.g., to a variable-speedmotor 104. The system 100 includes a controller 108, e.g., amicroprocessor, computer, printed circuit board (PCB), etc., configuredto provide a driver signal timed in accordance with a frequency of athree-line, three-phase power supply 112 to the motor 104. Line voltages116 a, 116 b, and 116 c of the power supply 112 provide power to themotor 104.

Interface circuits 120 a, 120 b, and 120 c are provided between avoltage input 122 and load 128 of each line (116 a, 116 b, 116 c). Eachinterface circuit (120 a, 120 b, 120 c) is configured to detect zerocrossings of the input voltage of the corresponding line (116 a, 116 b,116 c). Each interface circuit (120 a, 120 b, 120 c) enables or disablesinput through the corresponding line (116 a, 116 b, 116 c) based on thedriver signal from the controller 108.

Each interface circuit (120 a, 120 b, 120 c) includes, e.g., anopto-isolator 124, a zero crossing circuit 126, and a bidirectionalswitch, e.g., a triac 132 gated from the zero crossing circuit 126. Theopto-isolator 124 may be, e.g., a gallium arsenide (GaAs) infraredemitting diode optically coupled with the zero crossing circuit 126,e.g., a monolithic silicon detector, to perform as a zero voltagecrossing bilateral triac driver. In some embodiments the opto-isolator124, zero crossing circuit 126, and triac 132 are provided as a unit.One such unit is a six-pin zero-cross opto-isolators triac driver outputMOC3083M, available from Fairchild Semiconductor Corporation,www.fairchildsemi.com. The opto-isolators 124 of the interface circuits(120 a, 120 b, 120 c) are connected in series with the controller 108.

The system 100 also includes bidirectional switches, e.g., power triacs130, between the voltage input 122 and load 128 of each line (116 a, 116b, 116 c). The interface circuit (120 a, 120 b, 120 c) of each line (116a, 116 b, 116 c) is configured to trigger the corresponding power triac130 based on the driver signal from the controller 108 to enable ordisable power through the corresponding line (116 a, 116 b, 116 c) atzero crossings of the line voltage. In some configurations, each powertriac 130 has a blocking voltage of up to 800 volts and may be, e.g., asilicon bidirectional thyristor MAC8N, available from SemiconductorComponents Industries, LLC, http://onsemi.com. The controller 108 isconfigured to provide power to the motor 104 at each of a plurality ofspeeds, each speed defined by a corresponding number of cycles of acontrol duration of the driver signal.

In some embodiments, a control duration is eight cycles, and the speedsrange from zero up to and including a full speed defined by the eightcycles of the control duration. A timing diagram showing example driversignals that could be provided, e.g., to interface circuits (120 a, 120b, 120 c) in one eight-cycle control duration is indicated generally inFIG. 3 by reference number 200. Driver signals 204 range from a signal208 for zero (“0/8 ”) speed 212 up to and including a signal 216 forfull (“8/8”) speed 220. For zero speed 212, the driver signal 208 is setlow for each cycle 230 of the control duration. To provide a “1/8 ”speed 234 corresponding to one cycle of a voltage input 122, a driversignal 236 is set high for one cycle 230 and is set low for theremaining seven cycles. To provide a “2/8 ” speed 238 corresponding totwo cycles of a voltage input 122, a driver signal 240 is set high fortwo cycles 242 and is set low for the remaining six cycles. In similarfashion for other speeds “3/8 through 8/8”, a driver signal 204 is sethigh for the number of cycles corresponding to a desired speed and isset low for the remaining cycles, if any, of the control duration. Ofcourse, in other implementations the setting of a driver signal high orlow could have the opposite signification dependent, e.g., on a giveninterface circuit configuration. The driver signals 204 shown in FIG. 3are exemplary only, and that various control durations less than orgreater than eight cycles are possible, e.g., as discussed withreference to the signal 20 (shown in FIG. 1). Various patterns of highand low signals also are contemplated within a given control duration.

Referring again to FIG. 2, the system controller 108 provides a driversignal to the interface circuits (120 a, 120 b, 120 c) based on thefrequency of the line voltage input 122. In some implementations, thecontroller 108 may be preconfigured, e.g., programmed with software, toprovide the drive signal based on a commonly available line frequency,e.g., at 50 hertz and/or at 60 hertz. Additionally or alternatively, afrequency sensor circuit (e.g., an on board line frequency sensorcircuit) may be provided. For example, FIG. 4 illustrates an exemplaryembodiment of a frequency sensor circuit 300. In this example, thefrequency sensor circuit 300 receives an AC signal 304 from a step-downtransformer (not shown) connected with a line input voltage (116 a, 116b, 116 c). Such a transformer may be, e.g., a 24 VAC/60 Hz step-downtransformer. The signal 304 accordingly has a lower voltage but the samefrequency as that of the line voltage (116 a, 116 b, 116 c). The sensorcircuit 300 provides a square wave signal 308 at the same frequency asthe line voltage (116 a, 116 b, 116 c) to an input/output port (notshown) of the controller 108. Additionally or alternatively, linefrequency may be sensed directly from the AC line voltage (116 a, 116 b,116 c) by using an operational amplifier proportional circuit (notshown) to reduce the voltage. The reduced voltage signal is sent througha comparator (not shown) to obtain a square wave signal to thecontroller 108.

A motor may be provided with power, e.g., in accordance with oneimplementation of a driver signal control method indicated generally inFIG. 5 by reference number 400. The method 400 includes a main process404 performable over one control duration and that may be iterativelyperformed by the controller 108 to control the driver signal. Referringto FIGS. 2 and 4, if the motor 104 (FIG. 2) is switched on as indicatedin process 408 (FIG. 2), then in process 412, the currently selectedspeed of the motor 104 is obtained. In process 416, a timer of thecontroller 108 is enabled to time an interval equal to the number ofcycles of a line voltage (116 a, 116 b, 116 c) of the three-phase powersupply 112 corresponding to the selected speed. For example, if thespeed is “2/8 ” and the line voltage is at 50 hertz, the timer is set to40 milliseconds.

As indicated by process 420, the driver signal is output high or lowbased on the currently selected speed and the current cycle of thecontrol duration. Continuing the same example in which the speed hasbeen set to “2/8 ,” if the current cycle is the first of the controlduration, the driver signal is set high. On the other hand, if thecurrent cycle is the third of the eight cycles in the current controlduration, the driver signal output is low in process 420. If the driversignal is set high, it remains high, as indicated by process 424, untilthe high signal has lasted for two cycles, as indicated by process 428,whereupon the signal is brought low in process 432, the timer isdisabled in process 436, and control returns to the main process 404

Example values for various components of the system 100 are set forth inTable 1.

TABLE 1 R1, R5, R8 - 360 ohms R3, R6, R9 - 620 ohms R4, R7, R11 - 1Kohms R2 - 43 ohms R10 - 10K ohms Q4 - NPN silicon driver transistor,MMBTA06L RV1, RV2, RV3 - 680 volts C1, C2, C3 - 0.01 farads Q5 - NPNamplifier, MPSA05 R12 - 100K ohms R13 - 10K ohms R14 - 56K ohms

Based on implementations of the above motor control method, two blowersmay be used in a drying unit, e.g., a curing barn. As shown in FIGS. 6through 8, two blowers 504, 516 may be allocated in a drying unit 502.The blower 504 is at the upper side 508 for circulating air to the uppertobacco leaves 512. The blower 516 is close to the bottom 520 for bettercirculation to the bottom tobacco leaves 524.

A condenser 528 is placed in the middle of the drying unit 502. There isa damper 532 to suck outside fresh air for de-humidification purposes.An evaporator 536 also is provided outside the drying unit 502.

Most of the time, there may be only one blower running. The two blowers(504, 516) may in turn be switched to ON/OFF. When the upper blower 504is running, the air will be pushed down such that the upper tobaccoleaves will be close to the heat source and thus be hotter. When thebottom blower 516 is running, the air will be pushed up such that thebottom side tobacco leaves will be hotter. By doing such sequence, theinside temperature may be even (or substantially even) and motor powerconsumption is low.

In some extreme conditions like leaf rib drying, the CFM needed can bevery high. A reverse running capability can be added. For example, a3-phase motor may be reversed by reversing any two of the phases. Thetwo blowers (504, 516) can be ON at the same time, but one blower willbe push, while the other is pull. The two motors can be fully utilizedto maximize the CFM.

By way of example only, exemplary embodiments of methods and systemsdisclosed herein may provide one or more of the following advantagesover other ways of controlling and varying motor speed:

-   -   Low cost: Cost of triac based variable speed control is lower        than inverter type control; and/or    -   No harmonic noises: Zero-cross triggering method together with        full sine wave control; and/or    -   Power saving: 8 stage speed variation with reverse running logic        can reduce the blower power consumption; and/or    -   Higher reliability: Compared to inverter and random trigger type        triac control method, exemplary embodiments of this disclosure        may be less complex and robust.        The above mentioned possible advantages are provided for        purposes of illustration only, and do not limit the scope of the        present disclosure. Exemplary embodiments of methods and systems        disclosed herein may provide one or more of the above        advantages, all of the above advantages, none of the above        advantages, or combinations thereof.

In accordance with aspects of the present disclosure, exemplaryembodiments are disclosed of methods and apparatus for operating a motor(e.g., AC motor) in a variable speed situation using a step-wise methodof control. In an exemplary embodiment, a method includes determiningthe frequency of the AC power (e.g., 50 or 60 hertz), then determining abase unit of time based on the period of the frequency. After the baseunit of time is determined, it is multiplied by a whole number (8 inthis example) to get the operational time period. Then to operate themotor at lowest speed, the drive circuit is enabled for 1/8 of the totaltime period. For full speed, the drive circuit is enabled for 8/8 of thetotal time period. For example, if line frequency is 50 hertz, then thebase time period would be 0.020 seconds, and the total operationalperiod would be 0.160 seconds for 8 segments. The frequency forms thebasis for operation in this example as the drive circuitry is triggeredby zero crossing of the AC waveform. Also in this example, three drivecircuits may be used to create a variable speed AC motor control,enabling the drive circuit using the frequency to generate a base timeperiod for operation. The circuit in this example may sense theoperational frequency, and then determine the units it will use tooperate the circuit in the manner described above. In an exemplaryembodiment of a system or apparatus for operating a motor (e.g., ACmotor) in a variable speed situation, a system may include one or morephase circuits each of which is enabled as a function of time derivedarbitrarily from the frequency.

In an exemplary embodiment, a method of controlling a variable-speedmotor includes defining a control duration as a predetermined number ofcycles of a multiple-phase power supply; defining each speed in a rangeof speeds by a corresponding number of the cycles of the controlduration; and providing power to a motor from the multiple-phase powersupply at a selected one of the speeds, by enabling input from themultiple-phase power supply for the number of the cycles of the controlduration corresponding to the selected speed. Also in this example,enabling the power input from the multiple-phase power supply maycomprise driving a signal to switch input from lines of themultiple-phase power supply between “on” and “off” states atzero-crossing points of the cycles of the multiple-phase power supply.The method may also further comprise, for the control duration, causinginput from the lines to be in the “on” state only for the number of thecycles of the control duration corresponding to the selected speed. Thecycles may be full-wave cycles; and/or the control duration may bedefined as eight cycles of the power supply; and/or the method mayfurther comprise determining the duration of the cycles of the powersupply; and/or the motor may be included in a blower. The method may beperformed to control motors of first and second blowers where the firstblower is positioned above the second blower inside a drying unit inwhich a condenser is positioned between the first and second blowers anda damper is configured to admit air into the drying unit. The method mayfurther comprise alternating operation of the first and second blowersto alternate a direction of circulation in the drying unit; and/orsubstantially simultaneously operating one of the first and secondblowers in a forward direction and the other one of the first and secondblowers in a reverse direction.

In another exemplary embodiment, a method of controlling avariable-speed motor includes using a frequency of a multiple-phasepower supply to define a control duration having a fixed number ofcycles; defining each of a plurality of speeds as a corresponding numberof the cycles of the control duration; and providing power to a motorfrom the multi-phase power supply at a selected one of the plurality ofspeeds, by driving a signal configured in accordance with the frequencyto enable input from lines of the multi-phase power supply for thenumber of cycles of the control duration corresponding to the selectedspeed. The cycles may be full-wave cycles; and/or the control durationmay be defined as eight cycles of the power supply; and/or the methodmay further comprise determining the duration of the cycles of the powersupply; and/or the motor may be included in a blower. The method may beperformed to control motors of first and second blowers where the firstblower is positioned above the second blower inside a drying unit inwhich a condenser is positioned between the first and second blowers anda damper is configured to admit air into the drying unit. The method mayfurther comprise alternating operation of the first and second blowersto alternate a direction of circulation in the drying unit; and/orsubstantially simultaneously operating one of the first and secondblowers in a forward direction and the other one of the first and secondblowers in a reverse direction.

In another exemplary embodiment, a system for controlling avariable-speed motor includes a controller configured to provide adriver signal configured in accordance with a frequency of amultiple-line, multiple-phase power supply to a motor. The system alsoincludes an interface circuit between an input and load of each line.Each interface circuit is configured to detect zero crossings in thecorresponding line, and to enable or disable power through thecorresponding line at the zero crossings based on the driver signal. Thecontroller may be further configured to provide power to the motor ateach of a plurality of speeds, with each speed defined by acorresponding number of cycles of a control duration of the driversignal. The control duration may comprise eight cycles; and the speedsmay range from a zero speed up to and including a full speed defined bythe eight cycles of the control duration. The system may furthercomprise a bidirectional switch between the input and load of thecorresponding line, and the interface circuit may be further configuredto enable or disable power through the corresponding line at the zerocrossings by triggering the bidirectional switch. The system may beconfigured to control a motor of a blower. The system may be operablefor controlling a motor of at least one blower associated with orincluded in a tobacco curing barn. The tobacco curing barn may includefirst and second blowers with the first blower positioned above thesecond blower inside a drying unit in which a condenser is positionedbetween the first and second blowers and a damper is configured to admitair into the drying unit. The system may be operable for controllingmotors of the first and second blowers, including alternating operationof the first and second blowers to alternate a direction of circulationin the drying unit; and/or substantially simultaneously operating one ofthe first and second blowers in a forward direction and the other one ofthe first and second blowers in a reverse direction.

Example embodiments are provided so that this disclosure will bethorough, and will fully convey the scope to those who are skilled inthe art. Numerous specific details are set forth such as examples ofspecific components, devices, and methods, to provide a thoroughunderstanding of embodiments of the present disclosure. It will beapparent to those skilled in the art that specific details need not beemployed, that example embodiments may be embodied in many differentforms (e.g., different materials may be used, etc.) and that neithershould be construed to limit the scope of the disclosure. In someexample embodiments, well-known processes, well-known device structures,and well-known technologies are not described in detail.

Specific dimensions, specific materials, and/or specific shapesdisclosed herein are example in nature and do not limit the scope of thepresent disclosure. The disclosure herein of particular values andparticular ranges of values for given parameters are not exclusive ofother values and ranges of values that may be useful in one or more ofthe examples disclosed herein. Moreover, it is envisioned that any twoparticular values for a specific parameter stated herein may define theendpoints of a range of values that may be suitable for the givenparameter (i.e., the disclosure of a first value and a second value fora given parameter can be interpreted as disclosing that any valuebetween the first and second values could also be employed for the givenparameter). Similarly, it is envisioned that disclosure of two or moreranges of values for a parameter (whether such ranges are nested,overlapping or distinct) subsume all possible combination of ranges forthe value that might be claimed using endpoints of the disclosed ranges.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting. As usedherein, the singular forms “a”, “an” and “the” may be intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. The terms “comprises,” “comprising,” “including,” and“having,” are inclusive and therefore specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof. The method steps, processes, and operations described hereinare not to be construed as necessarily requiring their performance inthe particular order discussed or illustrated, unless specificallyidentified as an order of performance. It is also to be understood thatadditional or alternative steps may be employed.

When an element or layer is referred to as being “on”, “engaged to”,“connected to” or “coupled to” another element or layer, it may bedirectly on, engaged, connected or coupled to the other element orlayer, or intervening elements or layers may be present. In contrast,when an element is referred to as being “directly on,” “directly engagedto”, “directly connected to” or “directly coupled to” another element orlayer, there may be no intervening elements or layers present. Otherwords used to describe the relationship between elements should beinterpreted in a like fashion (e.g., “between” versus “directlybetween,” “adjacent” versus “directly adjacent,” etc.). As used herein,the term “and/or” includes any and all combinations of one or more ofthe associated listed items.

Although the terms first, second, third, etc. may be used herein todescribe various elements, components, regions, layers and/or sections,these elements, components, regions, layers and/or sections should notbe limited by these terms. These terms may be only used to distinguishone element, component, region, layer or section from another region,layer or section. Terms such as “first,” “second,” and other numericalterms when used herein do not imply a sequence or order unless clearlyindicated by the context. Thus, a first element, component, region,layer or section discussed below could be termed a second element,component, region, layer or section without departing from the teachingsof the example embodiments.

Spatially relative terms, such as “inner,” “outer,” “beneath”, “below”,“lower”, “above”, “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. Spatiallyrelative terms may be intended to encompass different orientations ofthe device in use or operation in addition to the orientation depictedin the figures. For example, if the device in the figures is turnedover, elements described as “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the example term “below” can encompass both an orientation ofabove and below. The device may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein interpreted accordingly.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements, intended orstated uses, or features of a particular embodiment are generally notlimited to that particular embodiment, but, where applicable, areinterchangeable and can be used in a selected embodiment, even if notspecifically shown or described. The same may also be varied in manyways. Such variations are not to be regarded as a departure from thedisclosure, and all such modifications are intended to be includedwithin the scope of the disclosure.

What is claimed is:
 1. A method of controlling a variable-speed motor,the method comprising: defining a control duration based on apredetermined number of cycles of an alternating current (AC) linefrequency; defining each speed in a range of speeds by a correspondingfraction of the control duration; a controller providing a driver signalto an interface circuit for each of one or more phases of an AC powersupply, to enable line voltage input to a variable-speed motor at the ACline frequency from the one or more phases for the fraction of thecontrol duration corresponding to a selected one of the speeds; and eachinterface circuit detecting zero-crossing points of the line voltageindependently of the controller and switching the line voltage inputfrom the corresponding phase between “on” and “off” states at detectedzero-crossing points of the line voltage input, such that an “on” timeof each interface circuit of the one or more interface circuitcorresponds to the fraction of the control duration corresponding to theselected one of the speeds, wherein the controller provides the driversignal to the interface circuit for each of the one or more phases ofthe AC power supply independently of the detecting of zero-crossingpoints of the line voltage by each interface circuit.
 2. The method ofclaim 1, wherein enabling line voltage input to the variable-speed motorfrom the AC power supply comprises enabling line voltage input from asingle phase or from three phases.
 3. The method of claim 1, wherein thedetecting of zero-crossing points of the line voltage by each interfacecircuit is performed by a zero cross circuit of the interface circuit.4. The method of claim 1, further comprising: the controller commencingthe driver signal to one of the one or more interface circuits betweenconsecutive first and second zero crossings of the AC power supply phasecorresponding to the one of the one or more interface circuits; and theone of the one or more interface circuits switching the line voltageinput from the corresponding phase at the detected second zero crossing.5. The method of claim 1, wherein: the control duration is defined aseight cycles of the AC line frequency, and the range of speeds aredefined by a corresponding number of the eight cycles, including a zerospeed defined by 0/8 cycles, a minimum or low speed defined by 1/8cycles, and a maximum or top speed defined by 8/8 cycles.
 6. A method ofcontrolling a variable-speed motor, the method comprising: a controllerproviding a driver signal to an interface circuit for a time periodequal to a fraction of a number of AC line voltage cycles by which afull-speed driver signal to the motor is defined, the fractioncorresponding to a selected motor speed; and the driver signal enablingthe interface circuit to switch a line voltage input to the motor on oroff upon detection of zero-crossing of the line voltage input by azero-crossing circuit of the interface circuit, the interface circuitbeing enabled to switch on the line voltage input to the motor, at theline voltage frequency for the time period equal to the fractioncorresponding to the selected motor speed; the driver signal to theinterface circuit being provided by the controller independent of thedetection of zero-crossing of the line voltage input.
 7. The method ofclaim 6, further comprising using a length of one of the AC cycles todefine a control duration corresponding to the full-speed drive signal;and defining each of a plurality of speeds as a corresponding number ofthe cycles of the control duration.
 8. The method of claim 6, whereinthe interface circuit detects zero-crossing points of the line voltageindependently of the controller and switches the line voltage inputbetween “on” and “off” states at detected zero-crossing points of theline voltage input.
 9. The method of claim 6, wherein: the number of ACline voltage cycles is eight AC cycles; and the method includes definingeach of a plurality of speeds as a corresponding fraction of the eightAC cycles, including a zero speed defined by 0/8 AC cycles, a minimum orlow speed defined by 1/8 AC cycles, and a maximum or top speed definedby 8/8 AC cycles.
 10. The method of claim 6, wherein: the line voltageinput comprises a plurality of line voltage inputs to the motor; theinterface circuit comprises a plurality of interface circuits; themethod includes the plurality of interface circuits collectivelyswitching on the plurality of line voltage inputs to the motor, wherebyan “on” time of each of the plurality of interface circuits is the timeperiod equal to the fraction corresponding to the selected motor speed.11. A system for controlling a variable-speed motor, the systemcomprising: a controller configured to provide a driver signalconfigured in accordance with an AC line frequency; and one or moreinterface circuits each configured to deliver a corresponding one of oneor more AC line voltage inputs to a load, each interface circuit havinga corresponding zero-crossing circuit configured to detect zero crossingin the corresponding line voltage input; each interface circuitconfigured to: receive the driver signal from the controller; and basedon the driver signal and the AC line frequency, enable or disable,collectively with the other one or more interface circuits, thecorresponding line voltage input at the detection of zero crossing bythe interface circuit; the detection of zero crossing being performedindependent of the drive signal.
 12. The system of claim 11, wherein thecontroller is further configured to provide power to the motor at eachof a plurality of speeds, each speed defined by a corresponding numberof cycles of a control duration of the driver signal.
 13. The system ofclaim 11, further comprising a bidirectional switch corresponding toeach interface circuit, the one or more interface circuits comprise aplurality of interface circuits configured to collectively enable ordisable power through the corresponding line voltage inputs at thedetection of zero crossing, by triggering the bidirectional switches.14. The system of claim 11, wherein the controller is configured toprovide the driver signal independently of the detection of zerocrossing.
 15. The system of claim 11, wherein the one or more linevoltage inputs comprise a single line voltage input and the one or moreinterface circuits comprise a single interface circuit.
 16. The systemof claim 11, wherein: the one or more AC line voltage inputs to a loadcomprise a plurality of AC line voltage inputs to the load; and the oneor more interface circuits comprise a plurality of interface circuitsconfigured to collectively enable or disable enable or disable the ACline voltage inputs to the load based on the driver signal and the ACline frequency.
 17. The system of claim 11, wherein the system isconfigured to: determine a frequency of the AC power line; determine abase unit of time based on a period of the frequency of the AC powerline; and determine an operational time period by multiplying the baseunit of time by a whole number; define a range of speeds bycorresponding fractions of the operational time period; and enable theone or more AC line voltage inputs for an “on” time corresponding to thefraction of the operational time period corresponding to a selected oneof the speeds.
 18. The method of claim 1, wherein: the line voltageinput comprises a plurality of line voltage inputs to the variable-speedmotor; the interface circuit comprises a plurality of interfacecircuits; the method includes the plurality of interface circuitscollectively enabling the plurality of line voltage inputs to thevariable-speed motor, whereby an “on” time of each of the plurality ofinterface circuits is the corresponding fraction of the control durationcorresponding to the selected one of the speeds.
 19. The method of claim1, wherein the method includes: determining a frequency of the AC powerline; determining a base unit of time based on a period of the frequencyof the AC power line; defining the control duration by multiplying thebase unit of time by a whole number; and enabling the line voltage inputfor an “on” time corresponding to the fraction of the control durationcorresponding to a selected one of the speeds.
 20. The system of claim12, wherein: the control duration comprises eight cycles of the AC linefrequency; and each of the plurality of speeds is defined as acorresponding fraction of the eight cycles, such that the speeds rangefrom a zero speed defined by 0/8 cycles, a minimum or low speed definedby 1/8 cycles, up to and including a full speed defined by the eightcycles (8/8 cycles) of the control duration.